In recent years, some mobile terminals such as cellular phones include an input device provided with a touch panel, touch switch, or other such touch sensor as an input device for detecting operation input by a user via an operation unit, switches, or the like. Input devices provided with a touch sensor are in wide use apart from mobile terminals as well, in information devices such as calculators or ticket vending machines, household appliances such as microwave ovens, televisions, or lighting appliances, industrial devices (factory automation equipment), and the like.
A variety of types of such touch sensors are known, such as a resistive film type, capacitive type, optical type, or the like. All of these types of touch sensors, however, simply detect contact by a finger, stylus pen, or the like. Upon being contacted, the touch sensor itself is not physically displaced like a mechanical push-button switch.
Since the touch sensor itself is not physically displaced even when contacted, the operator cannot receive any feedback regarding input even when the input device detects contact. Therefore, the operator acquires no sense of operation of a “push/release of a push” when providing operation input and is likely to provide input repeatedly by contacting the same position over and over, which may be stressful for the operator.
In order to prevent such unnecessary repetitive input, some devices for example generate a sound upon detecting contact. Other known devices allow for auditory or visual confirmation of the result of operation input via, for example, a change in the display state, such as a change in the display color of an input object (referred to below simply as an “object”), such as an input button, displayed as an image on a display unit in correspondence with the input position.
In the case of auditory feedback, however, confirmation becomes difficult in a noisy environment, and such feedback is not feasible if the device in use is muted, as during silent mode or the like. Furthermore, with visual feedback, if the size of the object displayed on the display unit is small, the operator may not be able to confirm the change in display state, particularly when input is provided by finger and the object is blocked from view by the finger.
To address this issue, a feedback method that is neither auditory nor visual but rather causes the touch sensor to vibrate when the touch sensor detects operation input, thus transmitting vibration to the operator's fingertip or the like, has also been proposed (for example, see Patent Literature 1 and 2).